regulator: core: streamline supply resolution for always-on/boot-on regulators

For always-on and boot-on regulators, regulator_register() is currently
trying to anticipate the requirement to resolve a supply early.

Unfortunately, this code executes too early, before we have potentially
updated the regulator's always_on constraint as part of
set_machine_constraints(), causing it to miss cases.

Rather than trying to hack it more, just defer to the outcome of
set_machine_constraints(). The latter returns early (without doing any
regulator initialisation) with -EPROBE_DEFER as of commit 'regulator:
core: move supply check earlier in set_machine_constraints()' and is
therefore safe to call multiple times to determine if supplies need to
be resolved early.

Commit 8a866d5 ("regulator: core: Resolve supply name earlier to
prevent double-init") (later updated by
commit 520fb17 ("regulator: core: Fix regulator supply
registration with sysfs")) added these tests originally to avoid
calling set_machine_constraints() multiple times to try to avoid
voltage glitches due to all the regulator initialisation happening each
time. This isn't an issue anymore as per above.

Signed-off-by: André Draszik <andre.draszik@linaro.org>
Link: https://patch.msgid.link/20260109-regulators-defer-v2-4-1a25dc968e60@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: andred

drivers/regulator/core.c

@@ -5937,7 +5937,6 @@ regulator_register(struct device *dev,
 	bool dangling_cfg_gpiod = false;
 	bool dangling_of_gpiod = false;
 	int ret, i;
-	bool resolved_early = false;
 
 	if (cfg == NULL)
 		return ERR_PTR(-EINVAL);
@@ -6075,17 +6074,6 @@ regulator_register(struct device *dev,
 			goto wash;
 	}
 
-	if ((rdev->supply_name && !rdev->supply) &&
-		(rdev->constraints->always_on ||
-		 rdev->constraints->boot_on)) {
-		ret = regulator_resolve_supply(rdev);
-		if (ret)
-			rdev_dbg(rdev, "unable to resolve supply early: %pe\n",
-					 ERR_PTR(ret));
-
-		resolved_early = true;
-	}
-
 	if (config->ena_gpiod) {
 		ret = regulator_ena_gpio_request(rdev, config);
 		if (ret != 0) {
@@ -6099,9 +6087,10 @@ regulator_register(struct device *dev,
 	}
 
 	ret = set_machine_constraints(rdev);
-	if (ret == -EPROBE_DEFER && !resolved_early) {
-		/* Regulator might be in bypass mode and so needs its supply
-		 * to set the constraints
+	if (ret == -EPROBE_DEFER) {
+		/* Regulator might be in bypass mode or an always-on or boot-on
+		 * regulator and so needs its supply to set the constraints or
+		 * for enable.
 		 */
 		/* FIXME: this currently triggers a chicken-and-egg problem
 		 * when creating -SUPPLY symlink in sysfs to a regulator